Fix up previous commit

- Apply the logic to the FreeBSD block
- Fix a typo with the getconf(1) call that I would have caught, were
  it not for the fact that I got the blocks wrong.
- Consolidate the hardcoded buffer sizes to the NetBSD block.

This would have been discovered had I run the test on a system where
PATH_MAX != 1024 (I don't have that at my disposal right at this moment).

MFC after:	3 weeks
MFC with:	r318210
Sponsored by:	Dell EMC Isilon

contrib/netbsd-tests/lib/libc/ssp/t_ssp.sh

@@ -386,14 +386,15 @@ read_body()
 {
 	prog="$(atf_get_srcdir)/h_read"
 
-	h_pass "$prog 1024" "echo foo |"
 	# Begin FreeBSD
 	if true; then
-		h_fail "$prog 1027" "echo bar |"
+	MAX_PATH=$(getconf _XOPEN_PATH_MAX) || atf_fail "getconf failed"
+	h_pass "$prog $MAX_PATH" "echo foo |"
+	h_fail "$prog $(( $MAX_PATH + 3 ))" "echo bar |"
 	else
 	# End FreeBSD
-	MAX_PATH=$(getconf _XOPEN_MAX_PATH) || atf_fail "getconf failed"
-	h_fail "$prog $(( $MAX_PATH + 1))" "echo bar |"
+	h_pass "$prog 1024" "echo foo |"
+	h_fail "$prog 1025" "echo bar |"
 	# Begin FreeBSD
 	fi
 	# End FreeBSD